When installing LM14 Cinnamon or Mate (64bit or 32bit), on an HP nc6400 notebook that supports PAE, the install hangs every time during the initial listing at:[1.854885][drm] Driver supports precise vblank timestamp query.

An older HP nc6230 laptop will install LM14 (32bit) with no problems, both have ATI graphics.

Sorry, what do you mean by "initial listing". Do you mean while booting up from the Linux Mint installation DVD or USB stick? If so, you might want to try and press a key during the 10 second countdown screen at boot. Then select the second entry in the menu, "Start in compatibility mode".

Linux Mint 13 64bit (Cinnamon or Mate) works very well on this laptop and I may have to leave it at 13...

When I attempt to install LM 14, cinnamon, mate, kde and either 32 or 64 bit, the system stalls during the initial boot at the same place every time.

Please see this image:

Can someone give me a suggestion or two? Is there some compatibility issue with 14 that there wasn't with 13? I was able to install 14 (32bit) on a slightly older HP nc6230 laptop (Pentium M), so I'm curious as to why I can't install it on the nc6400.

As detailed on LinLap (http://www.linlap.com/hewlett-packard_nc6400), your laptop's graphics card is probably not supported by the open source driver (the one Linux Mint comes preinstalled with). So follow the instructions here viewtopic.php?f=46&t=122257, and see if you can manage to boot successfully that way. Then install Linux Mint and install the proprietary graphics card driver as detailed.